Refrigeration cycle apparatus

ABSTRACT

A refrigeration cycle apparatus according to the present invention performs cooling by circulation of refrigerant. The refrigeration cycle apparatus includes an evaporator, a condenser, a pump, a compressor, and a controller. The evaporator is arranged in a first space. The condenser is arranged in a second space. The pump is configured to compress refrigerant from the condenser and output the refrigerant to the evaporator. The compressor is configured to compress refrigerant from the evaporator and output the refrigerant to the condenser. The controller is configured to control the pump and the compressor to cool the first space. The controller is configured to turn on the pump after turn-on of the compressor while a temperature of the first space is higher than a temperature of the second space.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. application Ser. No.16/336,557, filed Mar. 26, 2019, which is a U.S. national stageapplication of PCT/JP2016/087366 filed on Dec. 15, 2016, the contents ofwhich are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a refrigeration cycle apparatus whichperforms a low-outdoor-temperature cooling operation.

BACKGROUND

A cooling operation by a refrigeration cycle apparatus may be continuedfor a certain period regardless of an outdoor air temperature. In anexample of a server room where a server computer is operatingsubstantially throughout a year, if increase in temperature in theserver room due to heat generation from the server computer is leftunaddressed, processing capability of the server computer may be loweredand the server computer may fail and be shut down. In order to preventsuch a situation, a cooling operation by a refrigeration cycle apparatusis normally performed throughout a year in the server room.

In a cooling operation performed when an outdoor air temperature islower than a reference temperature (for example, 7° C.) (alow-outdoor-temperature cooling operation), an indoor temperature isnormally higher than an outdoor temperature. Therefore, liquidrefrigerant can evaporate in an evaporator in a room by making use of adifference between an indoor temperature and an outdoor temperature. Insuch a case, as in an air-conditioner disclosed in Japanese PatentLaying-Open No. 2000-193327 (PTL 1), a refrigeration cycle (a liquidpump cycle) with the use of a pump (a liquid pump) which compressesliquid refrigerant from an outdoor condenser and outputs the liquidrefrigerant to an indoor evaporator may be performed instead of arefrigeration cycle by a compressor (a vapor compression cycle). Theliquid pump cycle can achieve more suppressed power consumption than thevapor compression cycle.

Patent Literature

Japanese Patent Laid-Open Application No. 2000-193327

An amount of liquid refrigerant necessary in a liquid pump cycle isgreater than an amount of liquid refrigerant necessary in a vaporcompression cycle by an amount of compression of liquid refrigerant bythe liquid pump. When an amount of liquid refrigerant is insufficient,refrigerant suctioned by the liquid pump becomes wet vapor in agas-liquid two-phase state and cavitation is highly likely occur in theliquid pump. Cavitation is a phenomenon of generation of gas refrigerantin refrigerant. When cavitation occurs in the liquid pump, the liquidpump may fail and it may be difficult to continue alow-outdoor-temperature cooling operation.

SUMMARY

The present invention was made to solve the problem as described aboveand an object thereof is to improve stability of alow-outdoor-temperature cooling operation.

A refrigeration cycle apparatus according to the present inventionperforms cooling by circulation of refrigerant. The refrigeration cycleapparatus includes an evaporator, a condenser, a pump, a compressor, anda controller. The evaporator is arranged in a first space. The condenseris arranged in a second space. The pump is configured to compress therefrigerant from the condenser and output the refrigerant to theevaporator. The compressor is configured to compress the refrigerantfrom the evaporator and output the refrigerant to the condenser. Thecontroller is configured to control the pump and the compressor to coolthe first space. The controller is configured to turn on the pump afterturn-on of the compressor while a temperature of the first space ishigher than a temperature of the second space.

In a refrigeration cycle apparatus according to the present invention,while a temperature of a first space is higher than a temperature of asecond space, a pump which performs a liquid pump cycle is turned onafter turn-on of a compressor. As a vapor compression cycle is performedby the compressor before turn-on of the pump, a rate of generation ofliquid refrigerant in a condenser increases and an amount of liquidrefrigerant from the condenser increases. Consequently, occurrence ofcavitation in the pump is suppressed and stability in alow-outdoor-temperature cooling operation can be improved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a functional block diagram showing a configuration of arefrigeration cycle apparatus according to a first embodiment.

FIG. 2 shows together a time chart of a frequency of a liquid pump and atime chart of a frequency of a compressor in the first embodiment.

FIG. 3 is a diagram showing a hardware configuration of a controller inFIG. 1.

FIG. 4 is a P-h diagram showing relation between a pressure and enthalpyof refrigerant during a period in which a liquid pump remains off and avapor compression cycle is performed in FIG. 2.

FIG. 5 is a P-h diagram showing relation between a pressure and enthalpyof refrigerant during a period in which both of the vapor compressioncycle and a liquid pump cycle are performed in FIG. 2.

FIG. 6 is a P-h diagram showing relation between a pressure and enthalpyof refrigerant during a period in which a compressor remains off and theliquid pump cycle is performed in FIG. 2.

FIG. 7 is a functional block diagram showing a configuration of arefrigeration cycle apparatus according to a second embodiment.

FIG. 8 shows together a time chart of a frequency of the liquid pump, atime chart of a frequency of the compressor, and a time chart of adegree of opening of an expansion valve in the second embodiment.

FIG. 9 is a P-h diagram showing relation between a pressure and enthalpyof refrigerant during a period in which the liquid pump remains off andthe vapor compression cycle is performed in FIG. 8.

FIG. 10 is a P-h diagram showing relation between a pressure andenthalpy of refrigerant during a period in which both of the vaporcompression cycle and the liquid pump cycle are performed in FIG. 8.

FIG. 11 is a P-h diagram showing relation between a pressure andenthalpy of refrigerant during a period in which the compressor remainsoff and the liquid pump cycle is performed in FIG. 8.

FIG. 12 is a functional block diagram showing a configuration of arefrigeration cycle apparatus according to a third embodiment.

FIG. 13 shows together a time chart of a frequency of the liquid pump, atime chart of a frequency of the compressor, and a time chart of adegree of opening of an expansion valve in the third embodiment.

FIG. 14 is a P-h diagram showing relation between a pressure andenthalpy of refrigerant during a period in which the liquid pump remainsoff and the vapor compression cycle is performed in FIG. 13.

FIG. 15 is a P-h diagram showing relation between a pressure andenthalpy of refrigerant during a period in which both of the vaporcompression cycle and the liquid pump cycle are performed in FIG. 13.

FIG. 16 is a P-h diagram showing relation between a pressure andenthalpy of refrigerant during a period in which the compressor remainsoff and the liquid pump cycle is performed in FIG. 13.

FIG. 17 is a functional block diagram showing a configuration of arefrigeration cycle apparatus according to a modification of the thirdembodiment.

DESCRIPTION OF EMBODIMENTS

An embodiment of the present invention will be described in detail belowwith reference to the drawings. The same or corresponding elements inthe drawings have the same reference characters allotted and descriptionthereof will not be repeated in principle.

First Embodiment

FIG. 1 is a functional block diagram showing a configuration of arefrigeration cycle apparatus 100 according to a first embodiment. Asshown in FIG. 1, refrigeration cycle apparatus 100 includes an indoorunit 10 arranged indoors and an outdoor unit 20 arranged outdoors.Refrigeration cycle apparatus 100 performs a low-outdoor-temperaturecooling operation.

Indoor unit 10 includes a compressor 1, an evaporator 3, an indoor fan5, and a bypass flow path 11. Outdoor unit 20 includes a condenser 2, anoutdoor fan 4, a liquid pump 6, a controller 30, and a temperaturesensor 40. Controller 30 may be included in indoor unit 10 or may beincluded in neither of indoor unit 10 and outdoor unit 20.

Liquid pump 6 compresses liquid refrigerant (liquid refrigerant) fromcondenser 2 and outputs the refrigerant to evaporator 3. Controller 30controls a drive frequency of liquid pump 6 and controls an amount ofrefrigerant discharged per unit time.

Evaporator 3 evaporates liquid refrigerant from liquid pump 6. Inevaporator 3, liquid refrigerant evaporates by removing heat (heat ofvaporization) from indoor air and becomes gaseous refrigerant (gasrefrigerant), and gas refrigerant flows out of evaporator 3.

Compressor 1 compresses gas refrigerant from evaporator 3 and outputsthe refrigerant to condenser 2. Controller 30 controls a drive frequencyof compressor 1 and controls an amount of refrigerant discharged perunit time.

Bypass flow path 11 connects a flow path between evaporator 3 andcompressor 1 and a flow path between compressor 1 and condenser 2 toeach other. Bypass flow path 11 is connected in parallel to compressor 1between evaporator 3 and condenser 2. Bypass flow path 11 includes acheck valve 7. Check valve 7 allows refrigerant to pass when a pressureof refrigerant in the flow path between evaporator 3 and compressor 1 ishigher than a pressure of refrigerant in the flow path betweencompressor 1 and condenser 2.

Outdoor fan 4 sends air to condenser 2 for promoting heat exchangebetween refrigerant and air in condenser 2. Controller 30 controls arotation speed of outdoor fan 4 and controls an amount of air sent perunit time.

Indoor fan 5 sends air to evaporator 3 for promoting heat exchangebetween refrigerant and air in evaporator 3. Controller 30 controls arotation speed of indoor fan 5 and controls an amount of air sent perunit time.

Temperature sensor 40 measures a temperature of refrigerant betweencondenser 2 and liquid pump 6. Temperature sensor 40 is implemented, forexample, by a thermistor.

Controller 30 controls compressor 1, liquid pump 6, outdoor fan 4, andindoor fan 5. Controller 30 calculates a degree of supercooling ofrefrigerant from condenser 2 upon receiving a signal from temperaturesensor 40.

When an amount of liquid refrigerant necessary in a liquid pump cycle isinsufficient, refrigerant suctioned by liquid pump 6 becomes wet vaporin a gas-liquid two-phase state and cavitation is highly likely to occurin liquid pump 6. When cavitation occurs in liquid pump 6, liquid pump 6may fail and it may be difficult to continue a low-outdoor-temperaturecooling operation.

In the first embodiment, a vapor compression cycle is performed bycompressor 1 for a certain period of time and thereafter liquid pump 6is turned on. As shown in FIG. 2, compressor 1 performs the vaporcompression cycle before turn-on of liquid pump 6, a rate of generationof liquid refrigerant is increased and an amount of liquid refrigerantfrom condenser 2 is increased. Consequently, occurrence of cavitation inliquid pump 6 is suppressed and stability of a low-outdoor-temperaturecooling operation can be improved.

FIG. 2 shows together a time chart of a frequency of liquid pump 6 and atime chart of a frequency of compressor 1 in the first embodiment. Asshown in FIG. 2, controller 30 turns on compressor 1 at time tm1 andperforms the vapor compression cycle during a period S1 from time tm1 totm2. During period S1, an amount of refrigerant from condenser 2 isinsufficient and cavitation is highly likely to occur. Therefore,controller 30 turns off liquid pump 6. Controller 30 turns on liquidpump 6 at time tm2. During a period S2 from time tm2 to tm3, controller30 gradually increases a frequency of liquid pump 6 over time andgradually lowers a frequency of compressor 1 over time. During periodS2, controller 30 simultaneously performs the liquid pump cycle and thevapor compression cycle. During a period S3 after time tm3, controller30 turns off compressor 1 and controls liquid pump 6 to perform theliquid pump cycle while it maintains the frequency of liquid pump 6.

FIG. 3 is a diagram showing a hardware configuration of controller 30 inFIG. 1. Controllers 32, 33, and 33A described in second and thirdembodiments are also in a hardware configuration shown in FIG. 3.

As shown in FIG. 3, controller 30 includes processing circuitry 91, amemory 92, and an input/output unit 93. Processing circuitry may beimplemented by dedicated hardware or a central processing unit (CPU)that executes a program stored in memory 92. When processing circuitry91 is implemented by dedicated hardware, for example, a single circuit,a composite circuit, a programmed processor, a parallel-programmedprocessor, an application specific integrated circuit (ASIC), a fieldprogrammable gate array (FPGA), or combination thereof falls underprocessing circuit 91. When processing circuitry 91 is implemented bythe CPU, functions of controller 30 are performed by software, firmware,or combination of software and firmware. Software or firmware isdescribed as a program and stored in memory 92. Processing circuitry 91reads and executes a program stored in memory 92. Memory 92 includes anon-volatile or volatile semiconductor memory (for example, a randomaccess memory (RAM), a read only memory (ROM), a flash memory, anerasable programmable read only memory (EPROM), or an electricallyerasable programmable read only memory (EEPROM)), and a magnetic disc, aflexible disc, an optical disc, a compact disc, a mini disc, or adigital versatile disc (DVD). The CPU may also be referred to as acentral processing unit, a processing unit, an arithmetic unit, amicroprocessor, a microcomputer, a processor, or a digital signalprocessor (DSP).

Input/output unit 93 receives an operation from a user and provides aresult of processing to the user. Input/output unit 93 includes, forexample, a mouse, a keyboard, a touch panel, a display, and/or aspeaker.

FIG. 4 is a P-h diagram (Mollier diagram) showing relation between apressure and enthalpy of refrigerant during period S1 in FIG. 2. Duringperiod S1, the vapor compression cycle by compressor 1 is performedwhereas liquid pump 6 remains off. Curves IS1 and IS2 in FIG. 4represent isothermal lines of refrigerant corresponding to an outdoorair temperature T1 and an indoor temperature T2 (T1>T2), respectively. Acurve LC represents a saturated liquid line of refrigerant. A curve GCrepresents a saturated vapor line of refrigerant. A point CP representsa critical point of refrigerant. The critical point is a pointindicating a limit of a range where phase change between liquidrefrigerant and gas refrigerant may occur and an intersection betweenthe saturated liquid line and the saturated vapor line. When a pressureof refrigerant is higher than a pressure at the critical point, phasechange between liquid refrigerant and gas refrigerant no longer occurs.In a region where enthalpy is lower than the saturated liquid line,refrigerant is liquid. In a region lying between the saturated liquidline and saturated vapor line, refrigerant is in a state of wet vapor.In a region where enthalpy is higher than the saturated vapor line,refrigerant is gaseous. This is also applicable to FIGS. 4 and 5, FIGS.8 to 10 showing a second embodiment, and FIGS. 13 to 15 showing a thirdembodiment.

A cycle C11 in which circulation in the order of a point R11 to a pointR14 is performed represents circulation of refrigerant during period S1in FIG. 2. As shown in FIG. 4, cycle C11 is performed in a state that anindoor temperature is higher than an outdoor air temperature. This isalso applicable to cycles C12 and C13 in FIGS. 4 and 5, C21 to C23 inFIGS. 8 to 10 showing the second embodiment, and C31 to C33 in FIGS. 13to 15 showing the third embodiment.

A process of change in state from point R11 to a point R12 represents aprocess of compression of refrigerant by compressor 1. A pressure andenthalpy of refrigerant in a state at point R12 are higher than apressure and enthalpy of refrigerant in a state at point R11 owing tocompression by compressor 1.

A process of change in state from point R12 to a point R13 represents aprocess of condensation of refrigerant by condenser 2. A difference intemperature between refrigerant in a state at an intersection R15between a process of condensation and saturated liquid line LC andrefrigerant in a state at end point R13 of the process of condensationexpresses a degree of supercooling SC of refrigerant at point R13.Degree of supercooling SC is represented as a value of by how manydegrees refrigerant has further lowered since liquefaction ofrefrigerant. Refrigerant in a state at point R13 is suctioned by liquidpump 6 when the liquid pump is turned on.

A process of change in state from point R13 to point R14 represents aprocess for refrigerant to pass from condenser 2 through liquid pump 6which remains off and reach evaporator 3. Since pressure loss occursduring passage of refrigerant through a pipe and liquid pump 6 whichremains off, a pressure lowers in the process from point R13 to pointR14. A process of change in state from point R14 to point R11 representsa process of evaporation of refrigerant by evaporator 3.

Through the vapor compression cycle by compressor 1 during period S1, arate of generation of liquid refrigerant in condenser 2 increases, anamount of gas refrigerant in condenser 2 decreases, and an amount ofliquid refrigerant increases. Consequently, a quantity of heat absorbedfrom liquid refrigerant to outdoor air increases and degree ofsupercooling SC of refrigerant which flows out of condenser 2 increases.As degree of supercooling SC of refrigerant suctioned by liquid pump 6is higher, a state of refrigerant is more distant from a region in agas-liquid two-phase state and hence cavitation is less likely in liquidpump 6. In the first embodiment, when degree of supercooling SC ofrefrigerant in the state at point R13 is higher than a reference value,liquid pump 6 is turned on based on the determination that refrigerantsuctioned by liquid pump 6 is no longer in the gas-liquid two-phasestate and refrigerant has sufficiently been liquefied. The referencevalue can be calculated as appropriate through experiments with actualmachines or simulation.

FIG. 5 is a P-h diagram showing relation between a pressure and enthalpyof refrigerant during period S2 in FIG. 2. During period S2, the vaporcompression cycle by compressor 1 is continued and liquid pump 6 isturned on. Cycle C12 in which circulation in the order of points R21 toR24 in FIG. 5 is performed represents circulation of refrigerant duringperiod S2 in FIG. 2. A process of change in state from point R21 to apoint R22 represents a process of compression of refrigerant by liquidpump 6. A pressure and enthalpy of refrigerant in a state at point R22are higher than a pressure and enthalpy of refrigerant in a state atpoint R21 owing to compression by liquid pump 6.

A process of change in state from point R22 to a point R23 represents aprocess of evaporation of refrigerant by evaporator 3. A process ofchange in state from point R23 to point R24 represents a process ofcompression of refrigerant by compressor 1. A process of change in statefrom point R24 to point R21 represents a process of condensation ofrefrigerant by condenser 2.

When a frequency of liquid pump 6 is abruptly increased, an amount ofrefrigerant suctioned by liquid pump 6 abruptly increases. Therefore,the amount of refrigerant suctioned by liquid pump 6 may become greaterthan an amount of liquid refrigerant generated in condenser 2. In thatcase, cavitation is more likely to occur in liquid pump 6. Then,controller 30 gradually increases an amount of refrigerant suctioned byliquid pump 6 by increasing over time a frequency of liquid pump 6.

When a frequency of compressor 1 is abruptly lowered, an amount ofliquid refrigerant generated in condenser 2 abruptly decreases.Therefore, an amount of liquid refrigerant generated in condenser 2 maybecome smaller than an amount of refrigerant suctioned by liquid pump 6.In that case as well, cavitation is more likely to occur in liquid pump6. Then, controller 30 gradually decreases an amount of liquidrefrigerant generated in condenser 2 by lowering over time a frequencyof compressor 1.

During period S2, a pressure of refrigerant in a state at end point R22of the process of compression by liquid pump 6 (a starting point of theprocess of evaporation) and a pressure at end point R23 of the processof evaporation increase over time.

FIG. 6 is a P-h diagram showing relation between a pressure and enthalpyof refrigerant during period S3 in FIG. 2. During period S3, compressor1 is off whereas the liquid pump cycle by liquid pump 6 is continued.Cycle C13 in which circulation in the order of a point R31 to a pointR34 in FIG. 6 is performed represents circulation of refrigerant duringperiod S3 in FIG. 2. A process of change in state from point R31 to apoint R32 represents a process of compression of refrigerant by liquidpump 6. A process of change in state from point R32 to a point R33represents a process of evaporation of refrigerant by evaporator 3.

A process of change in state from point R33 to point R34 represents aprocess for refrigerant to pass from evaporator 3 through check valve 7and reach condenser 2. During period S3, compressor 1 is off and hence apressure of refrigerant in the flow path between evaporator 3 andcompressor 1 is higher than a pressure of refrigerant in the flow pathbetween compressor 1 and condenser 2. Most of refrigerant enters bypassflow path 11 low in pressure resistance, passes through check valve 7,and bypasses compressor 1. Most of refrigerant passes through bypassflow path 11 while the compressor is off so that refrigerant can beprevented from staying in compressor 1 which remains off. In a processof change in state from point R33 to point R34, a pressure ofrefrigerant in a state at point R34 is lower than a pressure ofrefrigerant in a state at point R33 due to pressure loss caused duringpassage of refrigerant through a pipe and the check valve. A process ofchange in state from point R34 to point R31 represents a process ofcondensation of refrigerant by condenser 2.

A condition for turn-on of liquid pump 6 in the first embodiment is thatdegree of supercooling SC exceeds a reference value. A condition forturn-on of liquid pump 6 may be any condition so long as it can bedetermined that refrigerant suctioned by liquid pump 6 is no longer inthe gas-liquid two-phase state and refrigerant has sufficiently beenliquefied, and for example, it may be a condition that an operation bycompressor 1 continues for a reference period of time.

In the first embodiment, bypass flow path 11 includes a check valve.Bypass flow path 11 does not necessarily have to include a check valve,and it may be configured in any manner so long as refrigerant is allowedto pass when a pressure of refrigerant in the flow path betweenevaporator 3 and compressor 1 is higher than a pressure of refrigerantin the flow path between compressor 1 and condenser 2. For example, itmay be configured such that bypass flow path 11 includes an on-off valveand controller 30 controls the on-off valve to open when a pressure ofrefrigerant in the flow path between evaporator 3 and compressor 1 ishigher than a pressure of refrigerant in the flow path betweencompressor 1 and condenser 2.

In the refrigeration cycle apparatus according to the first embodiment,the liquid pump which performs the liquid pump cycle is turned on afterturn-on of the compressor. As the compressor performs the vaporcompression cycle before turn-on of the liquid pump, a rate ofgeneration of liquid refrigerant in the condenser increases and anamount of liquid refrigerant from the condenser increases. Consequently,occurrence of cavitation in the liquid pump is suppressed and stabilityof a low-outdoor-temperature cooling operation can be improved.

According to the first embodiment, since refrigerant bypasses thecompressor by passing through the bypass flow path while the compressorremains off, refrigerant can be prevented from staying in the compressorwhich remains off.

According to the first embodiment, when a degree of supercooling ofrefrigerant suctioned by the liquid pump is higher than a referencevalue, the controller turns on the liquid pump so that occurrence ofcavitation in the liquid pump can further be suppressed.

According to the first embodiment, the controller increases over time anamount of refrigerant discharged per unit time by the liquid pump afterturn-on of the liquid pump and decreases over time an amount ofrefrigerant discharged per unit time by the compressor after turn-on ofthe liquid pump, so that occurrence of cavitation in the liquid pump canfurther be suppressed.

According to the first embodiment, the indoor fan promotes heat exchangein the evaporator and the outdoor fan promotes heat exchange in thecondenser. Therefore, a rate of generation of liquid refrigerant in thecondenser in the vapor compression cycle is increased. Consequently,start of the liquid pump cycle can be earlier.

Second Embodiment

An example in which refrigerant from the liquid pump flows into theevaporator through a pressure regulation valve will be described in asecond embodiment. The second embodiment is different from the firstembodiment in that the pressure regulation valve is connected betweenthe liquid pump and the evaporator. Since the second embodiment isotherwise similar, description will not be repeated.

FIG. 7 is a functional block diagram showing a configuration of arefrigeration cycle apparatus 200 according to the second embodiment. Inrefrigeration cycle apparatus 200 shown in FIG. 7, indoor unit 10 andcontroller 30 in FIG. 1 are replaced with an indoor unit 12 and acontroller 32, respectively. As shown in FIG. 7, indoor unit 12 includesan expansion valve 8 as the pressure regulation valve in addition to thefeatures included in indoor unit 10 shown in FIG. 1. Expansion valve 8is connected between liquid pump 6 and evaporator 3. A degree of openingof expansion valve 8 is adjusted by controller 32. Expansion valve 8 isimplemented, for example, by an electronically controlled expansionvalve (a linear expansion valve: LEV).

FIG. 8 shows together a time chart of a frequency of liquid pump 6, atime chart of a frequency of compressor 1, and a time chart of a degreeof opening of expansion valve 8 in the second embodiment. Periods S21 toS23 in FIG. 8 correspond to periods S1 to S3 in FIG. 2, respectively.Since operations by compressor 1 and liquid pump 6 during periods S21 toS23 are the same as in the first embodiment, description will not berepeated. As shown in FIG. 8, a degree of opening of expansion valve 8is set to a reference degree of opening d1 at time tm21 at whichcompressor 1 is on. A degree of opening of expansion valve 8 increasesuntil the expansion valve is fully opened over time. Reference degree ofopening d1 can be determined as appropriate through experiments withactual machines or simulation.

A degree of opening of expansion valve 8 may be adjusted, for example,such that a degree of superheating of refrigerant suctioned intocompressor 1, a degree of superheating of refrigerant discharged fromcompressor 1, or a temperature of refrigerant discharged from compressor1 attains to a reference value. A degree of opening of expansion valve 8may be adjusted such that a difference in pressure between refrigerantdischarged by liquid pump 6 and suctioned refrigerant attains to areference value. A degree of opening of expansion valve 8 may beadjusted such that a degree of supercooling of refrigerant which flowsout of condenser 2 attains to a reference value.

FIG. 9 is a P-h diagram showing relation between a pressure and enthalpyof refrigerant during period S21 in FIG. 8. Cycle C21 in whichcirculation in the order of points R211 to R214 in FIG. 9 is performedrepresents circulation of refrigerant during period S21 in FIG. 8. Aprocess of change in state from point R211 to a point R212 represents aprocess of compression of refrigerant by compressor 1. A process ofchange in state from point R212 to a point R213 represents a process ofcondensation of refrigerant by condenser 2. A process of change in statefrom point R213 to point R214 represents a process of decompression ofrefrigerant by expansion valve 8. A process of change in state frompoint R214 to point R211 represents a process of evaporation ofrefrigerant by evaporator 3.

Cycle C21 shown in FIG. 9 is similar to a cycle representing a normalcooling operation performed when an indoor temperature is lower than anoutdoor air temperature (for example, during summer). In the secondembodiment, expansion valve 8 decompresses refrigerant such thatrefrigerant can evaporate in a room even though the indoor temperatureis lower than the outdoor air temperature. The refrigeration cycleapparatus according to the second embodiment can perform a normalcooling operation in addition to the low-outdoor-temperature coolingoperation.

Liquid pump 6 is turned on when degree of supercooling SC of refrigerantin a state at point R213 is higher than a reference value also in thesecond embodiment. FIG. 10 is a P-h diagram showing relation between apressure and enthalpy of refrigerant during a period S22 in FIG. 8. Acycle C22 in which circulation from a point R221 to a point R225 in FIG.10 is performed represents circulation of refrigerant during period S22in FIG. 8. A process of change in state from point R221 to point R222represents a process of compression of refrigerant by liquid pump 6. Aprocess of change in state from point R222 to point R223 represents aprocess of decompression by expansion valve 8. A process of change instate from point R223 to point R224 represents a process of evaporationby evaporator 3. A process of change in state from point R224 to pointR225 represents a process of compression of refrigerant by compressor 1.A process of change in state from point R225 to point R221 represents aprocess of condensation of refrigerant by condenser 2.

During period S22, controller 32 increases over time a frequency ofliquid pump 6 and increases an amount of refrigerant suctioned by liquidpump 6 with increase in liquid refrigerant in condenser 2. A pressure ofrefrigerant in a state at end point R222 of the process of compressionby liquid pump 6 (a starting point of the process of decompression)increases over time. In the second embodiment, controller 32 increasesover time a degree of opening of expansion valve 8 to lower adecompression function of expansion valve 8. A pressure of refrigerantin a state at end point R223 of the process of decompression (a startingpoint of the process of evaporation) and a pressure of refrigerant in astate at end point R224 of the process of evaporation both increase.

FIG. 11 is a P-h diagram showing relation between a pressure andenthalpy of refrigerant during period S23 in FIG. 8. Cycle C23 in whichcirculation in the order of points R231 to R235 in FIG. 11 is performedrepresents circulation of refrigerant during period S23 in FIG. 8. Aprocess of change in state from point R231 to a point R232 represents aprocess of compression of refrigerant by liquid pump 6. A process ofchange in state from point R232 to a point R233 represents a process forrefrigerant from liquid pump 6 to pass through expansion valve 8 andreach evaporator 3. Since pressure loss occurs during passage ofrefrigerant through a pipe and expansion valve 8 that is fully opened, apressure lowers in the process from point R232 to point R233.

A process of change in state from point R233 to a point R234 representsa process of evaporation of refrigerant by evaporator 3. A process ofchange in state from point R234 to point R235 represents a process forrefrigerant from evaporator 3 to pass through check valve 7 and reachcondenser 2. A process of change in state from point R235 to point R231represents a process of condensation of refrigerant by condenser 2.

According to the refrigeration cycle apparatus according to the secondembodiment above, an effect the same as in the first embodiment can beobtained. Furthermore, in the second embodiment, refrigerant from thecondenser flows into the evaporator as being decompressed in the vaporcompression cycle (see FIG. 9) so that a difference between refrigerantin the evaporator and an indoor temperature is greater than in the firstembodiment and a difference between refrigerant in the condenser and anoutdoor temperature is also greater than in the first embodiment.Therefore, efficiency in heat exchange between refrigerant and air inthe evaporator and the condenser is enhanced and a rate of generation ofliquid refrigerant in the condenser is higher than in the firstembodiment. Consequently, time required for an amount of liquidrefrigerant from the condenser to be an amount required for the liquidpump cycle can be decreased and start of the liquid pump cycle can beearlier than in the first embodiment.

Third Embodiment

An example in which refrigerant from the compressor or the check valveflows into the condenser through a pressure regulation valve will bedescribed in a third embodiment. The third embodiment is different fromthe first embodiment in that a pressure regulation valve is connectedbetween the compressor and the condenser. Since the third embodiment isotherwise similar, description will not be repeated.

FIG. 12 is a functional block diagram showing a configuration of arefrigeration cycle apparatus 300 according to the third embodiment. Inrefrigeration cycle apparatus 300 shown in FIG. 12, outdoor unit 20 andcontroller 30 in FIG. 1 are replaced with an outdoor unit 23 and acontroller 33, respectively. As shown in FIG. 12, outdoor unit 23includes an expansion valve 9 as a pressure regulation valve in additionto features included in outdoor unit 20 shown in FIG. 1. Expansion valve9 is connected between compressor 1 and condenser 2. A degree of openingof expansion valve 9 is adjusted by controller 33. Expansion valve 9 isimplemented, for example, by an electronically controlled expansionvalve (a linear expansion valve: LEV).

FIG. 13 shows together a time chart of a frequency of liquid pump 6, atime chart of a frequency of compressor 1, and a time chart of a degreeof opening of expansion valve 9 in the third embodiment. Periods S31 toS33 in FIG. 13 correspond to periods S1 to S3 in FIG. 2, respectively.Since operations by compressor 1 and liquid pump 6 during periods S31 toS33 are the same as in the first embodiment, description will not berepeated. As shown in FIG. 13, controller 32 sets a degree of opening ofexpansion valve 9 to a reference degree of opening d2 at time tm31 atwhich compressor 1 is on. Controller 32 gradually increases a degree ofopening of expansion valve 9 until the expansion valve is fully openedover time. Reference degree of opening d2 can be determined asappropriate through experiments with actual machines or simulation.

A degree of opening of expansion valve 9 may be adjusted, for example,such that a degree of superheating of refrigerant suctioned intocompressor 1, a degree of superheating of refrigerant discharged fromcompressor 1, or a temperature of refrigerant discharged from compressor1 attains to a reference value. A degree of opening of expansion valve 9may be adjusted such that a difference in pressure between refrigerantdischarged by liquid pump 6 and suctioned refrigerant attains to areference value. A degree of opening of expansion valve 9 may beadjusted such that a degree of supercooling of refrigerant which flowsout of condenser 2 attains to a reference value.

FIG. 14 is a P-h diagram showing relation between a pressure andenthalpy of refrigerant during period S31 in FIG. 13. Cycle C31 in whichcirculation in the order of points R311 to R315 in FIG. 14 is performedrepresents circulation of refrigerant during period S31 in FIG. 13. Aprocess of change in state from point R311 to a point R312 represents aprocess of compression of refrigerant by compressor 1. A process ofchange in state from point R312 to a point R313 represents a process ofdecompression by expansion valve 9. A process of change in state frompoint R313 to a point R314 represents a process of condensation ofrefrigerant by condenser 2. A process of change in state from point R314to point R315 represents a process for refrigerant from condenser 2 topass through liquid pump 6 that remains off and reach evaporator 3. Aprocess of change in state from point R315 to point R311 represents aprocess of evaporation of refrigerant by evaporator 3.

Liquid pump 6 is turned on when degree of supercooling SC of refrigerantin a state at point R314 is higher than a reference value also in thethird embodiment. FIG. 15 is a P-h diagram showing relation between apressure and enthalpy of refrigerant during period S32 in FIG. 13. Acycle C32 in which circulation in the order of a point R321 to a pointR325 in FIG. 15 is performed represents circulation of refrigerantduring period S32 in FIG. 13. A process of change in state from pointR321 to a point R322 represents a process of compression of refrigerantby liquid pump 6. A process of change in state from point R322 to apoint R323 represents a process of evaporation of refrigerant byevaporator 3. A process of change in state from point R323 to a pointR324 represents a process of compression of refrigerant by compressor 1.A process of change in state from point R324 to point R325 represents aprocess of decompression of refrigerant by expansion valve 9. A processof change in state from point R325 to point R321 represents a process ofcondensation of refrigerant by condenser 2.

FIG. 16 is a P-h diagram showing relation between a pressure andenthalpy of refrigerant during period S33 in FIG. 13. Cycle C33 in whichcirculation in the order of points R331 to R334 in FIG. 16 is performedrepresents circulation of refrigerant during period S33 in FIG. 13. Aprocess of change in state from point R331 to a point R332 represents aprocess of compression of refrigerant by liquid pump 6. A process ofchange in state from point R332 to a point R333 represents a process ofevaporation of refrigerant by evaporator 3. A process of change in statefrom point R333 to a point R334 represents a process for refrigerantfrom evaporator 3 to pass through check valve 7 and reach condenser 2. Aprocess of change in state from point R334 to point R331 represents aprocess of condensation of refrigerant by condenser 2.

The refrigeration cycle apparatus according to the third embodimentabove can achieve an effect the same as in the first embodiment.Furthermore, in the third embodiment, in transition from a state thatthe vapor compression cycle and the liquid pump cycle are simultaneouslyperformed (see FIG. 15) to a state that the vapor compression cycle isstopped and the liquid pump cycle is performed (see FIG. 16), a pressureof refrigerant in the process of evaporation is higher than a pressureof refrigerant in the process of condensation, and relation in magnitudetherebetween is less likely to change. Therefore, in the refrigerationcycle apparatus according to the third embodiment, abrupt change inpressure is less likely to occur in transition from the vaporcompression cycle to the liquid pump cycle and the liquid pump cycle canbe continued in a stable manner.

In the refrigeration cycle apparatus according to the third embodiment,refrigerant from the compressor or the check valve flows into thecondenser as being decompressed by the pressure regulation valve.Therefore, a pressure in the process of condensation (a pressure ofrefrigerant suctioned by the liquid pump) is lower than in the first andsecond embodiments. Consequently, load imposed on the liquid pump byreceiving a pressure of refrigerant can be lessened.

FIG. 17 is a functional block diagram showing a configuration of arefrigeration cycle apparatus 300A according to a modification of thethird embodiment. In refrigeration cycle apparatus 300A shown in FIG.17, indoor unit 10 and controller 33 in FIG. 12 are replaced with indoorunit 12 and a controller 33A, respectively. Indoor unit 12 is similar toindoor unit 12 shown in FIG. 7 in connection with the second embodiment.Refrigeration cycle apparatus 300A can also obtain an effect the same asin the second and third embodiments.

Combination of embodiments disclosed herein as appropriate is alsointended unless combination is inconsistent. It should be understoodthat the embodiments disclosed herein are illustrative andnon-restrictive in every respect. The scope of the present invention isdefined by the terms of the claims rather than the description above andis intended to include any modifications within the scope and meaningequivalent to the terms of the claims.

1. A refrigeration cycle apparatus which performs cooling by circulationof refrigerant, the refrigeration cycle apparatus comprising: anevaporator arranged in a first space; a condenser arranged in a secondspace; a pump configured to compress the refrigerant from the condenserand output the refrigerant to the evaporator; a compressor configured tocompress the refrigerant from the evaporator and output the refrigerantto the condenser; and a controller configured to control the pump andthe compressor to cool the first space, the controller being configuredto turn on the pump after turn-on of the compressor while a temperatureof the first space is higher than a temperature of the second space and,control the pump to gradually increase an amount of the refrigerantdischarged per unit time by the pump during an elapsed time intervalfrom time when the pump is turned on.
 2. The refrigeration cycleapparatus according to claim 1, further comprising a bypass flow pathconfigured to connect a first flow path between the evaporator and thecompressor and a second flow path between the compressor and thecondenser to each other, and allow the refrigerant to pass when apressure of the refrigerant in the first flow path is higher than apressure of the refrigerant in the second flow path.
 3. Therefrigeration cycle apparatus according to claim 2, wherein the bypassflow path comprises a check valve configured to allow the refrigerant topass when the pressure of the refrigerant in the first flow path ishigher than the pressure of the refrigerant in the second flow path. 4.The refrigeration cycle apparatus according to claim 1, wherein thecontroller is configured to turn on the pump when a degree ofsupercooling of the refrigerant suctioned by the pump is higher than areference value.
 5. The refrigeration cycle apparatus according to claim4, further comprising a temperature sensor arranged in a third flow pathbetween the condenser and the pump, the temperature sensor beingconfigured to measure a temperature of the refrigerant in the third flowpath, wherein the controller is configured to calculate the degree ofsupercooling by using the temperature.
 6. The refrigeration cycleapparatus according to claim 1, wherein the controller is configured toturn on the pump in succession to an operation of the compressor whichcontinues for a reference period of time.
 7. The refrigeration cycleapparatus according to claim 1, wherein the controller controls thecompressor to decrease an amount of the refrigerant discharged per unittime by the compressor with an elapsed time interval from time when thepump is turned on.
 8. The refrigeration cycle apparatus according toclaim 1, further comprising: a first blower apparatus configured to sendair to the evaporator; and a second blower apparatus configured to sendair to the condenser.
 9. The refrigeration cycle apparatus according toclaim 1, further comprising a first pressure regulation valve connectedbetween the evaporator and the pump, wherein a degree of opening of thefirst pressure regulation valve is larger after turn-on than beforeturn-on of the compressor.
 10. The refrigeration cycle apparatusaccording to claim 9, wherein the degree of opening of the firstpressure regulation valve is set to a first reference degree of openingat turn-on of the compressor.
 11. The refrigeration cycle apparatusaccording to claim 9, further comprising a second pressure regulationvalve connected between the compressor and the condenser, wherein adegree of opening of the second pressure regulation valve is largerafter turn-on than before turn-on of the compressor.
 12. Therefrigeration cycle apparatus according to claim 11, wherein the degreeof opening of the second pressure regulation valve is set to a secondreference degree of opening at turn-on of the compressor.
 13. Therefrigeration cycle apparatus according to claim 1, further comprising apressure regulation valve connected between the compressor and thecondenser, wherein a degree of opening of the pressure regulation valveis larger after turn-on than before turn-on of the compressor.
 14. Therefrigeration cycle apparatus according to claim 13, wherein the degreeof opening of the pressure regulation valve is set to a reference degreeof opening at turn-on of the compressor.
 15. A refrigeration cycleapparatus, comprising: a refrigerant circuit comprising a compressor, afirst heat exchanger, a pump, and a second heat exchanger; and acontroller configured to perform a vapor compression cycle during afirst period S1 from a first time tm1 to a second time tm2, avapor-compression-and-liquid-pump cycle during a second period S2 fromthe second time tm2 to a third time tm3, and a liquid pump cycle duringa third period S3 starting at the third time tm3, wherein in the firstperiod S1, the controller is configured to turn on the compressor at thefirst time tm1 and the pump is off during the first period S1, in thesecond period S2, the controller is configured to turn on the pump atthe second time tm2, gradually increase a frequency of the pump from thesecond time tm2 to the third time tm3, and gradually decrease afrequency of the compressor from the second time tm2 to the third timetm3 until the compressor turns off at the third time tm3, and in thethird period S3, the controller is configured to maintain the frequencyof the pump at a constant frequency and the compressor is off during thethird period S3.
 16. The refrigeration cycle apparatus according toclaim 15, wherein the refrigerant circuit further comprises an expansionvalve, and in the first period S1, the controller is further configuredto gradually increase an opening degree of the expansion valve startingat the first time period tm1 from a reference opening degree until theopening degree reaches a fully-open opening degree.